Assignment: Analytical Summary: Clean Air Act
The below article explains the regional specifics (Northeastern US and in particular New England) of air pollution, wind currents, acid rain formation and ozone impacts, with the figures, and talks about their interrelationship. What I want you do is to read the article given below and write your own analytical summary on impacts of Clean Air Act on acid rain and anatomy of ozone in New England and post it in the assignment folder, marked as "STA-4" .
Acid rain and the Environmental Impact of the Clean Air Act
Ozone in New England
Northern New England's quality of life and business are routinely affected by changes in air quality. In fact, during summer, most of southern New Hampshire and coastal Maine suffer from episodic ozone events that are regarded as "very unhealthy" for humans and the environment. New England also suffers from the effects of acid rain. These and other air quality issues in the region are largely the result of the influx of airborne pollutants originating from industrial regions, metropolitan centers, and transportation corridors located in upwind source regions (especially in the Midwestern and mid-Atlantic United States), although emissions from within northern New England from transportation and industrial sources also play a key role. Recently, an analysis of air pollution, precipitation, and tropical cyclones along the eastern seaboard of the U.S. suggested that human activities are affecting weather patterns on a regional scale. An increased frequency of weekend storms has been linked to the buildup of air pollution during the week (Cerveny and Balling, 1998). An improved understanding of the relationships between weather, air-mass trajectories, air quality in northern New England, and human and ecosystem health is essential for maintaining our quality of life in the region.
Acid rain and the Environmental Impact of the Clean Air Act
Precipitation chemistry records derived from a Greenland ice core (Figure 1.3, Mayewski et al., 1990) reveal a dramatic increase in the concentrations of sulfate and nitrate following the industrial revolution (approximately 1900 AD), as mentioned in Chapter One. The Greenland ice core record also shows a leveling off of sulfate and nitrate concentrations after 1970 when the National Ambient Air Quality Standards (NAAQS) were established as part of the Clean Air Act . The 1970 amendments to the Federal Clean Air Act were developed to protect the public's health and welfare by controlling air pollution at its source through the establishment of primary and secondary NAAQS. Since 1970 several amendments have been made establishing stricter primary and secondary NAAQS as a result of a better understanding of the impact that air pollutants have on human health and the environment.
Acid rain is caused primarily by the emission of sulfur dioxide (SO2) and nitrogen oxides (NOx) from the combustion of fossil fuels that we use to heat our homes, power our cars, generate electricity, and run our factories. Here in the Northeast, this phenomenon has caused lakes and stream to become unsuitable for many fish (Baker and Schofield, 1985; Park, 1987). Acid rain has been known to leach heavy metals such as mercury from rocks, thereby causing contamination of water supplies and introducing human health risks (Brakke et al., 1988). Acid rain can also alter soil chemistry in agricultural and forested lands and causes significant damage to human made structures, especially those consisting of limestone and marble. In addition to contributing to acid rain, sulfate aerosols also play a significant role in Earth's radiation balance. The increase in sulfate aerosol in the troposphere adjacent to industrial regions of the globe over the past century has in fact served to cool climate on a regional scale (Charlson et al., 1992; Mayewski et al., 1993, IPCC, 1995).
How has the Clean Air Act affected the acid rain problem in the northeast?
Aerosol chemistry samples from Whiteface Mountain in upstate New York show a strong correlation between the decrease in SO2 emissions in the mid-western states since 1970 and the decrease in average sulfate concentrations in the Northeast (Husain et al., 1998). The deposition of sulfate in precipitation in northern New England measured at four locations has decreased on the order of 30% since the early 1980s (Figure 4.3a ). In addition, the longest precipitation chemistry record in New England, measured at Hubbard Brook in northern New Hampshire, shows that the average pH of precipitation has increased since 1970 from approximately 4.1 to 4.3 standard pH units (Figure 4.4 ), indicating that the acidity of precipitation is slowly decreasing. The same cannot be said for the deposition of nitrate, which has shown no significant change since the early 1980s (Figure 4.3b ).
The decrease in sulfate deposition and precipitation acidity can be directly linked to the reduction in SO2 emissions as a result of the Clean Air Act. In fact, annual SO2 emissions from anthropogenic sources in the U.S. have decreased from 28.3 million metric tons in 1970 to 17.4 million metric tons in 1996 (Figure 4.5 ). This is due primarily to a reduction in sulfur emissions from electric utilities, which are responsible for approximately two-thirds of the nation's sulfur emissions. At the same time, nitrogen oxides emission rates have increased from 19.7 million metric tons in 1970 to 21.3 million metric tons in 1996. This increase can largely be related to the more than doubling of vehicle miles traveled over the past three decades. (U.S.EPA, 1977). Motor vehicles currently account for approximately 30% of all nitrogen oxides emissions.
Clearly, the Clean Air Act Amendments have been successful in reducing sulfur oxides emission rates and sulfate deposition via precipitation. On the other hand, nitrogen oxides emission rates have continued to increase, albeit slowly, and wet deposition of nitrate has remained relatively constant. Amendments to the Clean Air Act that were designed to reduce emissions of criteria pollutants further were passed in 1990 and were phased in starting in 1995. Ongoing air quality monitoring and research programs will evaluate the effect of the 1995 amendments on air quality in coming years.
Ozone in New England:
Ozone is a very important chemical in our atmosphere. It is found in the troposphere (near the earth's surface, where our weather occurs) as well as in the stratosphere (above the troposphere). Ozone in the stratosphere protects us from ultraviolet radiation. Scientists are concerned about the depletion of this ozone layer, particularly the ozone "hole" over Antarctica, as well as the more recent depletion in northern latitudes. Ozone in the troposphere affects us very differently. Tropospheric ozone, a component of urban smog, causes health problems for humans and ecosystems. In high concentrations for periods of a few hours, ozone can damage lung tissue, reduce lung function, irritate eyes, and is also harmful to plants.
Tropospheric ozone is a pollutant which affects large geographical areas when weather conditions are favorable for its formation. Ozone at ground-level is a secondary pollutant which forms in the atmosphere as a by-product of chemical reactions that take place between other chemical compounds (i.e. ozone precursors) emitted from automobiles, diesel trucks and industrial sources. Specifically, these ozone precursors are volatile organic compounds (VOCs) and oxides of nitrogen (NOx). These compounds react together when exposed to strong ultraviolet radiation from the sun during hot summer weather.
Ozone, NOx , and VOCs are currently monitored by State Environmental Agencies. Several stations have been established in New England since several cities in the region (including the Dover-Portsmouth-Rochester region) are designated as "serious non-attainment zones" for ozone by the EPA. Very high ozone levels occur in the seacoast regions of Maine, New Hampshire, and Massachusetts during the summer due to a combination of factors. These areas are densely populated and produce an abundance of pollution themselves. The area also tends to be sunny in spring and summer because of the sea breeze effect, which inhibits cloud formation. However, ozone levels tend to rise to their highest and most unhealthy levels when pollutants are transported into New England from regions to the southwest along what is known as the ozone transport corridor.
In 1997, the EPA changed its criteria for unhealthy ozone levels. Instead of hourly ozone levels exceeding 120 parts per billion (ppb), an 8-hour average of over 80 ppb is now considered an "exceedance". Some individuals may be affected by short periods of very high ozone, but it is more harmful for most people and for plants to be exposed for longer periods of time, even at a lower level. This change in standards resulted in more events being classified as very unhealthy (Figure 4.6 ).
The high number of unhealthy ozone days in 1988 is remarkable. This is primarily attributed to a circulation pattern which brought several periods of hot sunny weather to the Northeast. This circulation pattern was linked to a phenomenon in the southern Pacific ocean called La Niña , which often follows a prolonged El Niño event. Interestingly, climate events halfway around the world have a significant effect on our region's air quality.
On average, southern New Hampshire and coastal Maine experience 3 to 5 days per year of very unhealthy ozone levels, with some years (e.g., 1988) that are considerably worse. However, high ozone levels are not restricted to these areas. In fact, very unhealthy levels of ozone have also been measured by the Appalachian Mountain Club (AMC) at the summit of Mount Washington.
What is the anatomy of a high ozone event in New England?
Below, we provide 3 examples of ozone events in New Hampshire to illustrate what we know and what we do not concerning the causes of high ozone events in the region.
1. High Ozone along the East Coast, June 28-July 1, 1997 :
On 28 June a high pressure center to the west of New England yielded sunny skies (Figure 4.7a ). Pollutants from the seacoast reacted with sunlight to form ozone. However, by 1 July, ozone levels increased by an additional 50%.
Why this increase?
As the high pressure system moved eastwards, the prevailing winds shifted from a northwest to a southwest direction, transporting pollutants and already-formed ozone from other industrial areas to the southwest and along the east coast of the U.S. (Figure 4.7b ), adding to already high ozone levels. The influence of ozone transported into coastal New Hampshire and Maine is clearly illustrated in Figure 4.8 . Ozone and its precursors move with the weather systems and ozone formed as a result of New York or Boston emissions can impact populations in New Hampshire and Maine on a hot summer day. The highest ozone levels of the day typically occurs late in the afternoon at monitoring stations most susceptible to long range transport. Coastal ozone monitors in New Hampshire and Maine usually record the highest ozone concentrations as a result of transport over the open ocean from the big cities to the south. Wind direction on a hot summer afternoon will determine if ground-level ozone is going to be a problem on a particular day. In addition, peak values for ozone rise steadily from 28 June to 1 July, as more polluted air is transported into the region (Figure 4.9 ). Note that the trend in NO2, one chemical compound which contributes to ozone formation, shows a trend which is opposite to that for ozone (i.e., low values during the afternoon when ozone levels are greatest). This illustrates NO2 consumption during the series of reactions that lead to the formation of ozone.
2. High Ozone at Portsmouth and Mt. Washington, 11 July 1988:
This was a period of very high ozone on the seacoast as well as on the summit of Mount Washington ( figure 4.10 ). As usual, the seacoast levels drop dramatically at night as tropospheric ozonewas effectively removed from the atmosphere close to the ground and because it is not produced after the sun goes down. Atop Mount Washington, though, the readings remained very high, actually peaking in the early morning on the 11th, and not dropping below 70 ppb for three straight days. The White Mountain region is not a major pollutant source, and therefore the ozone was probably carried in on westerly winds. The lack of a diurnal variation is explained by the fact that there is very little ground surface at the summit of Mt. Washington, so ozone is not readily removed from the atmosphere. Note that ozone levels at the base of the mountain were much lower than at the summit, day and night, even though it is only four miles away. The dense forest environment at the base serves to rapidly remove ozone from the atmosphere.
3. High ozone only on Mount Washington, 4-5 July, 1989:
Ozone levels on the summit of Mt. Washington peaked early on 5 July at about 130 ppb, well above normal and healthy levels. However, ozone levels at the base of the mountain and on the seacoast never exceeded 60 ppb. (figure 4.11 )
Why the difference between sites, and why did it peak in the early morning when ozone formation is normally highest in the afternoon?
Perhaps a disturbance in the layer that separates the troposphere from the stratosphere allowed ozone from the stratosphere ("good" ozone, our protective shield) to accumulate for a short period at the summit of Mt. Washington, but was not transported to low elevations such as the base of Mt. Washington or the seacoast. This peak may also represent the long-range transport of ozone from the west or southwest at elevations of 5000 - 6000 feet (i.e., the summit elevation of Mount Washington), which would not influence ozone concentration on the seacoast. Future monitoring of a variety of both gas phase and aerosol chemistry will provide the data necessary to answer these and other important scientific questions regarding air quality in New England.
Why continue to investigate air quality in New England?
Clearly, our general understanding of chemical climate in New England over the past two decades improved substantially - especially with respect to acid rain and ozone. However, many of the specifics regarding air quality issues remain poorly understood. In conjunction with ongoing air quality monitoring programs in the region, we plan to develop a detailed air quality/air-mass trajectory data base in order to address several specific scientific questions, including:
How much of the poor air quality that we suffer from in New England is the result of pollution produced locally verses pollution that is transported into the region from upwind sources (e.g., mid-west or mid-Atlantic states)? How much does this change over days, weeks, months, and seasons?
How will changes in the strength of these local and upwind sources (as mandated by the Clean Air Act) affect air quality in New England over the coming years?
What and where are the specific sources of pollution, and which weather patterns cause the worst air quality in New England?
Are there significant differences between air quality in the mountains and the seacoast regions of New England? Why?
How will the predicted warming of 2.5 o to 4 oC with a doubling of atmospheric carbon dioxide (IPCC, 1995), and the potential changes in precipitation and atmospheric circulation patterns, affect New England's chemical climate?
How will regional and long traveled pollution aerosol influence the Earth's radiation budget over New England?
Answers to these and other questions regarding the quality of the air we breathe are being sought through the examination of data collected from existing sites and that proposed at future sites. Results will provide us with the understanding to deal with air quality issues in the future.
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